Impact of Ultra-Low-Dose Imaging on Image Quality and Volumetric Accuracy of Different Subtypes of Pulmonary Nodules using Photon-Counting Detector CT: A Phantom Study

Purpose To evaluate the impact of ultra-high-resolution photon-counting detector CT (UHR PCD-CT) combined with ultra-low dose scanning protocol on the detection rate, image quality, diameter, and volumetric measurement accuracy of pulmonary nodules of varying sizes and types. Materials and Methods A thoracic phantom with 15 pulmonary nodule models was scanned on UHR PCD-CT at five dose levels. Quantitative analysis was performed on the detection rate, long-axis/short-axis diameters, noise value (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the nodules at each dose level. Pulmonary nodule AI diagnostic software was used to measure nodule volume and calculate the absolute percentage error in volume (APEvolume). Similarly, the absolute percentage error in diameter measurement (APEdiameter) was calculated. Subjective image quality was assessed using a 5-point scale, with images from the 1.00 mGy dose group as the reference. Results Dose reduction significantly lowered the detection rates of pulmonary nodules while increasing both APEdiameter and APEvolume. Solid nodules (SNs) exhibited better detectability compared to ground-glass nodules (GGNs), with nodules ≥6 mm showing superior performance over smaller lesions. Subjectively, performance at 0.50 mGy was clear but slightly worse than that at standard-dose (1.00 mGy) (all P < 0.05). Conclusion Even under ultra-low dose conditions (0.03-0.50 mGy), UHR PCD-CT combined with AI-assisted diagnostic software can still maintain the detection of pulmonary nodules and provide diagnostic-quality images. Advances in knowledge UHR PCD-CT is capable of yielding diagnostic image quality even at significantly reduced radiation doses, allowing for the confident assessment of specific nodule types and larger nodules.